This invention relates to a picture stablizing circuit for a video cassette recorder (hereinafter referred to as "VCR"). In particular, a picture stablizing circuit is designed for preventing instability caused by noise when a speed change occurs during a reproduction mode of the VCR.
In general, noise is produced when a speed change occurs during the reproduction mode of the VCR. If the noise corresponds to a synchronizing signal portion of the video signal, then the noise rapidly moves the picture in a vertical direction to the picture or vibrates the picture so that an unstable picture is produced.
In order to correct the unstable picture caused by the speed change during the reproduction mode of the VCR, the picture may be manipulated by the tracking adjustment unit that is mounted on the exterior of the VCR. By manipulating the tacking adjustment unit, the scanning position of the video head is adjusted so that the noise is not superposed on the synchronizing signal portion. However, if the reproduction mode is normally repeated, or if the speed changing direction is shifted, then the picture must be stabilized by repeating the manipulation of the tracking adjustment unit, which is complex and troublesome. This manipulation causes the vertical synchronizing signal to be lost and the picture to become unstable. Previously, a stable picture had been developed when the speed change during the reproduction mode produces a forced synchronizing signal synchronized to the head switching signal when the speed change occurs during the reproduction mode of the VCR. A vertical synchronizing portion of the video signal is produced by applying the forced synchronizing signal to the video signals. According to this conventional device, problems remain when noise is produced at the beginning of the forced synchonizing signals, and noise signals are treated similar to forced or vertical synchronizing signals. Consequently, the picture will temporarily shake or collapse and a substantially stable picture is impossible to produce.